I'm not so certain that's exactly how it'd go. OEMs faced with being forced to provide updates at an unknown pace might just decide to try to roll their own version of Play Services and the underlying data that those hook into, which given the quality of their normal bundleware isn't too promising.

And face the issue that key apps wouldn't run on their devices, thus making people not care about them.

As it already happened to a few that tried such attempts.

Amazon is probably the only one that can manage to push known app vendors to also publish on their store.